The present invention relates to an arrangement for forming layers from individual sheets and for transporting the formed layers in general, and more particularly to an arrangement for forming successive layers of sheets of paper and the like from a stream of individual sheets supplied in succession to a collecting location by a supplying conveyor, and for transferring the formed layers to a continuously advancing discharge conveyor.
Arrangements of this general type are already known and in widespread use. Usually, an arrangement of this type includes an abutment which is movable into and out of the trajectory or the sheets at the collecting location, a clamping device including positionally controllable jaws which is movable between the collecting location and the discharge conveyor, and a mechanical transmission by means of which the abutment and the clamping device are kinematically connected with one another as well as with a common drive.
An arrangement of this type is usually the last structural unit of a machine which operates in a predetermined cycle, to which there is connected another machine which may also operate in the predetermined machine cycle or may treat layers of sheets supplied thereto in an arbitrary rhythm. The operating cycle of the first mentioned machine is determined by the succession of cuts performed by a transverse cutter which cuts either a single paper web withdrawn from a single supply roll or a plurality of superimposed webs withdrawn from a corresponding number of supply rolls, into sheets of a defined length. In most instances, the discharge conveyor is formed by pairs of conveyor belts between which the formed layers of sheets are drawn by means of the clamping device. During the transfer of the layers to the conveyor belt pairs, the clamping device is supposed to at least approximately reach the speed of the conveyor belts. For this reason, the mechanical transmission which drives the clamping device and the abutment is kinematically connected to the discharge conveyor in such a manner as to operate in synchronism therewith. An arrangement of this type is shown, for instance, in the German published patent application DE-OS No. 2,508,745.
The cooperation of the abutment and the clamping device, as well as the operating speeds thereof, depend on the speed of advancement of the supplied sheets and hence on the machine speed and the number of the sheets which are collected in a given layer. The proportion of the machine cycle to the operating cycle of the arrangement determines the number of the sheets collected in a particular layer.
The conventional arrangements of this type are connected to the main drive of the machine by means of exchangeable wheels, so that the number of the sheets which are collected in a particular layer and which are transported in such layer by means of the clamping device, can be changed by utilizing different exchangeable wheels. Usually such wheels include meshing gears or the like. When this expedient is resorted to, it must be remembered that the jaws of the clamping device must close with a speed which is dependent on the spacing of the sheets relative to one another or on the extent of the so-called overlap and the advancing speed of the sheets. This is so inasmuch as the clamping device must grip the collected layer before the following sheet reaches its operating range. In the conventional arrangements, this is taken care of in that a control segment of a cam which controls the closing of the jaws of the clamping device is exchanged at the time that the exchangeable wheels are exchanged.
It will become apparent from the above discussion that the conversion of the arrangement is a very time-consuming task. In addition thereto, in order to be able to adapt the performance of the arrangement to the performance conditions or demands, it is necessary to obtain and store a multitude of exchangeable wheels or gears and corresponding control cam segments.
The impossibility of rapid conversion of the arrangement is particularly disadvantageous when a plurality of paper webs are superimposed in the machine upon one another and cut simultaneously so that, during a single machine cycle, for instance, five sheets are supplied through the collecting location at any time. Now, when it is desired to form layers containing 20 sheets, the clamping device must perform an operating cycle after each four machine cycles. Should one of the paper webs tear, or should it be established that one of the sheets is of inferior quality, the machine could continue its operation with the remaining four webs if it were possible to immediately adjust the arrangement with the clamping device in such a manner that it would perform an operating cycle at each five machine cycles. However, in view of the fact that, as explained above, this change-over or adjustment is very time consuming, one can just as well change the respective supply roll in approximately the same time as it would take to modify the transmission. Thus, whether changing the gears or other wheels of the transmission and the corresponding segments, or exchanging the defective supply roll or correcting the defect of the same, an extensive interruption of production is unavoidable.
There are also known arrangements in which the ratio of the operating cycle of the arrangement to the machine cycle can be changed without interruption of production by a simple adjustment of a counter. However, arrangements of this type are limited as to their output. In particular, they are not suited for handling sensitive papers, such as carbon papers. These arrangements include separate pneumatic drives for the individual function elements, such drives being controlled by a counter and a step-by-step control which is driven in the machine cycle. The use of the pneumatic drives is the reason for the limitation of the output of the arrangement, as well as for the abrupt clamping operation of the jaws of the clamping device which, as explained above, is detrimental to certain types of paper. On the other hand, such sensitive paper types can be handled by the device of the initially discussed kind.